Known optical sensors e.g. include a transmission unit for transmitting transmission light into a detection zone, a receiver for receiving light reflected back or remitted back from the detection zone and an evaluation unit for evaluating the light reflected back or remitted back. In this respect, it can e.g. be a question of scanner systems in which a light beam produced e.g. by a laser is deflected via a light deflection unit into a detection zone and is there reflected or remitted by an object which may be present. The reflected or remitted light moves back to the scanner again and is detected by a receiver there. The light deflection unit is frequently designed to be pivotable or rotatable such that the light beam produced by the laser sweeps over the detection zone produced by the pivot movement. If a reflected or remitted light signal received by the receiver is received, a conclusion can be drawn on the angular position of the object in the detection zone from the angular position of the deflection unit.
Other optical sensors are configured as distance-measuring sensors which can draw a conclusion on the distance of the object e.g. from the light duration which a light signal irradiated into a detection zone requires back to the sensor again after reflection at an object in the detection zone.
A combination of such a scanner system and of a distance-measuring sensor can be used to completely monitor two-dimensional protected fields. A deflection in a further spatial direction while using a plurality of such scaners with e.g. protected fields arranged in fan shape or in parallel with one another also allows the monitoring of a three-dimensional space (3D scanners).
Such systems are used e.g. in driverless transport systems to avoid collisions. Other applications relate e.g. to machines in which a danger zone has to be monitored which may not be infringed by an operator in the operation of the machine. It can in this respect e.g. be a robot working zone. If the presence of an unpermitted object—that is, for example, a leg of an operator—is detected in the danger zone with the help of the laser scanner, an emergency stop of the machine is effected.
Such scanner systems are e.g. described in DE 39 08 273 C1 or EP 1 980 871 B1.
Other optical systems are configured as light barriers or as light gratings which detect the presence of an object in a detection zone by interrupting a light beam or by reflection of the light beam from the detection zone.
A monitoring of the most important performance functions is necessary for checking the operability, in particular for the reliable object detection and object localization in a safety system. In this respect, in known solutions, test objects are provided in the monitored zone of the sensor. A test is made before or during the measurement of whether these test objects are correctly detected. An optical sensor is known from DE 198 00 968 C2, wherein for this purpose a test object arranged in the interior of the sensor housing is illuminated through a corresponding inlet window. A scanner is known from DE 39 08 273 C1 in which the detection ability of the sensor can be monitored by monitoring the positions of a plurality of offset external test targets having defined degrees of reflection.
The long-term stability of the system is important. The use of safety scanners is therefore frequently in particular problematic in the outdoor sector since contamination or moisture precipitation at the test object can result in a reduction in the detection reliability, which can result in an unforeseeable defective response of the scanner.